Page 47 - Soil Degradation, Conservation and Remediation

32 1 Soil Resources and Soil Degradation

are the common crops grown as monocrops. It is economically an effi cient system,
but it can negatively impact the soil fertility and ecology. The roots of the crop draw
the same kind and proportion of nutrients from the soil for a long period of time.
The nutrient status of the soil becomes imbalanced after a prolonged period of crop-
ping. Particular types of insects and pests proliferate. Farmers become increasingly
dependent on pesticides.

1.7.1.6 Mismanagement of Irrigation

It is not possible for farming to occur without artificial irrigation in arid lands where

there is a deficiency of moisture. However, irrigation in arid lands can further
enhance desertifi cation through salinization and alkalinization. Salinization occurs
when irrigation water evaporates quickly, leaving natural salts (chlorides, sulfates,
and carbonates of sodium, potassium, calcium, and magnesium) at the surface of the
soil. Over a long time, excessive quantities of salts accumulate at or near the soil

surface, making it increasingly difficult for plants to extract water from the soil.
This is because inadequate water is applied for the scarcity of water in the arid and
semiarid climate. Irrigation water must consider the leaching requirement (extra
water to leach the salts) of the soil.

1.7.1.7 Use of Heavy Farm Machineries

Heavy farm machineries are used in mechanized agriculture by the developed coun-
tries. Tractors and cultivators may weigh more than 20 tons. Such heavy loads of
these machines severely compact soils. This is almost irreversible. Deep compac-
tion below the plow layer (plow pan) is difficult to decompact. Impact of heavy farm

machineries on soil degradation is discussed in more detail in connection with soil
compaction (Chap. 2 ; Sect. 2.2.3.1).

1.7.1.8 Mining

Mining contributes significantly to soil pollution, especially with heavy metals.
The disposal of Cd from Zn mines in the water of Jintzu River in Japan and con-
tamination of soils and rice grains that caused the notorious itai-itai disease is a
good example. A soil survey conducted by Kurnia et al. ( 2000 ) in West Java
exhibited that the soil surrounding the traditional gold mining areas was polluted
by mercury. A high concentration of mercury was found in rice straw and rice
grain in that area. All of the values were higher than the maximum permitted level
−1
of Hg in soils (0.5 mg kg ). Mining is responsible for large-scale soil
degradation.